One passenger was pulled off a Detroit-bound plane in Miami Wednesday night for yelling “I want to kill all the Jews.” Another passenger on a flight to Hawaii Wednesday was so unruly that US jets were scrambled to shepherd the plane back to Portland, Ore.

Coming a few weeks after the foiled Christmas Day attack by an alleged Al Qaeda operative on Northwest Flight 253, the outbursts were enough to jangle nerves amid heightened vigilance at airports nationwide. But they were out of character for an airline industry that turned in one of its calmest years on record in 2009.

Last year was part of a five-year downward trend in unruly passenger incidents reported to the Federal Aviation Administration. The agency recorded a historic high of 304 incidents in 2004. As of Nov. 19, 2009, the latest figures available, the FAA reported only 88 cases.

“You won’t find a lot of incidents where a particular ethnic group is singled out and somebody goes on a tirade about killing them,” says Mr. Baker. “Something set him off and he had this hatred or animosity already building up and it was just a matter of somebody triggering it. We don’t have screens for these people going on airplanes and probably never will."

Moreover, police say Mr. Asad was sober. In the vast number of onboard disturbances, alcohol is the primary factor, experts say. The FBI eventually identified the incident as not a national security issue, but as a local police matter.

The incident on the Hawaii-bound plane was more typical, officials say. The jets were scrambled after “a suspicious passenger … made threatening remarks and refused to store his carry-on bag." But a spokeswoman for Hawaiian Airlines told Fox News: "This is kind of a routine passenger disturbance on board.... It's not of any paricular concern."

Why air rage reports are declining

The downward trend in reported air rage incidents could have several causes, experts say. Post-9/11 vigilance on the part of flight crews and authorities – rather than a spike in actual incidents – might explain the spike in 2004, Baker says.

Moreover, the flying public is aware that there might be undercover air marshals on planes, and that authorities could use deadly force if they fear a threat to the airplane. In 2005, for instance, air marshals shot and killed a man at Miami-Dade International Airport after he claimed he had a bomb in a backpack and ran away from authorities.

Passengers are also more likely to self-police flights since 9/11, jumping in “as soon as somebody sees somebody doing something suspicious,” Baker says.

It’s not clear what set Asad off, but Miami-Dade police detective Javier Baez said in a statement that passengers said he was “loud and disruptive, using anti-Semitic references such as, 'I’m Palestinian and I want to kill all the Jews.' ”

When police took Asad and three companions off the plane to be searched, the man continued his verbal rampage, berating officers with racist statements, including, “Go back to Africa, you white racist cop!” Police finally used a Taser to subdue him.